Numbers: The Sun, From Temperature to Solar Cycles to Fuel Supply

10,000 Temperature, in degrees Fahrenheit, at the sun’s surface. The core, a giant nuclear reactor, operates at 27 million degrees. Strangely, the corona, the sun’s outer atmosphere, is much hotter than its surface, surpassing 1 million degrees. A study published in January offered a possible explanation, showing that jets shooting out from the sun’s surface contain gas that is even hotter than previously realized.

600 Million Amount of hydrogen fuel, in tons, that the sun converts to helium and energy through nuclear fusion every second. That is equivalent to the weight of all the coal burned in the United States in seven months. At 4.5 billion years old, the sun has burned through nearly half its hydrogen fuel supply.

11 Duration, in years, of a typical solar cycle, natural variations in the number of sunspots and flares that affect solar irradiance levels on Earth. Sunspots, marked by dark areas on the sun, indicate a strong magnetic field. Solar flares are powerful explosions at the star’s surface. The current cycle began in 2008, and a NOAA panel predicts it will peak in May 2013. In the past, large solar flares have caused blackouts and disrupted communications on Earth.

1,000,000 Speed, in miles per hour, of the solar wind, a stream of charged particles flowing from the sun in all directions. A mission called Solar Probe Plus, slated to launch before 2018, will dive into the sun’s atmosphere to study how the wind achieves its astonishing speed. In September NASA selected the instruments, including a telescope and a particle counter, that will make the unprecedented journey.